Method of coating projector-lamps with reflecting-surfaces.



E. L. CLARK.

METHOD OF COATING PROJECTOR LAMPS WITH RBFLEGTING SURFACES.

APPLICATION FILED JAN. 11, 1913.

1,1 21,802. Patented Dec. 22, 1914;

WITNESSES INVENTOR EMERSON L. CLARK By $1M 4AM ATTORNEY UNITED STA ESArum OFFICE.

EMERSON-L. CLARK, OF LAKEWOOD, OHIO, ASSIGNOR TO NATIONAL CARBONCOMPANY, I

' OF CLEVELAND, OHIO, A CORPORATION OF NEW JERSEY.

METHOD OF COATING PROJECTOR-LAMPS WITH REFLECTING-SUBFAGES. 4

specification of Letters Patent, P ;2 9

Application filed January 11, 1913; Serial No. 741,373.

To all whom it may concern Be it known that I, EMERSON L. CLARK, acitizen of the United States, residing at Lakewood, in the county ofCuyahoga and State of Ohio, have invented a certam new and usefulImprovement in -Methods of Coating Projector-Lamps with Reflecting-Surfaces, of which the following is a fu 1, clear, and exactdescription.

My invention relates to a method for internally coating an incandescentlamp with a highly reflecting surface.

In my application filed October 17th, 1912, Serial No. 726204, forincandescent light for projection apparatus, I have disclosed animproved form of projector lamp of the incandescent' type.

This invention relates to a method of applying the reflecting coating onthe interior of the incandescent, lamp there disclosed.

Figure 1 is a more or less diagrammatic representation of means forcoating an incandescent lamp with reflecting material.

Fig. 2 is an end view of. the arrangement shown in Fig. 1 with means.for cooling certain parts of the lamp. Fig. 3 shows a modified form ofthe arrangement for coating the lamp. Fig. 4 illustrates a furthermodification.

If a source of light be partly surrounded by a difl'used reflectingsurface and the remaining area of the surfacebe composed; of a mediumpervious to light, all of the light emitted from the source musteventually proceeed through sucharea provided the efliciency of thereflecting surface is 100%. That is, if all the light is reflected backand forth from the reflecting surface and none of it is absorbed, itmust be all emitted through the light pervious area. However, a diffusedreflecting surface of 100% efliciency is not at present obtainable, sothat with the lamp constructedas described, the entire light emittedfrom the source would not pass out through the window or lightperviousarea, but a certain amount would be absorbed. The concentratingeffectproduced by such arrangement can be approximately computed as follows:Let I be the mean spherical intensity of the extended source within thereflecting inclosure; let R be the reflecting co-eificient of thereflecting inclosure; let P be the per cent. area which is uncoated withreflecting material; let 1' be the radius of the inclosure (assumed.reflecting property is-thus almost spherical). then'the intensity ofthe illumination produced at the light-pervious area or window is:

'. If, instead of a diffused reflecting surface,

apolished surface is used so that specular reflection 1s had and theinterior surface of means that only that part of the light would finallyreach the window that was reflected in the plane of the great circlesthat intersect it. But even with specular reflection, the intensity oflight would be greatly increased at the window. However, in practice, itwould be impossible to obtain a bulb with such an exact interior surfacethat the light rays would continue to be reflected in the plane in whichthey started. As a matter of fact, the interior surface would conslst ofm nute surfaces facing n diverse directions. This would be sufficient'tocause all'light to be eventually reflected through the window so thatthe light emitted through it would 'follow somewhat approximately thelawof diffused reflection. The interior of the bulb may be made with anirregular surface to cause the light to more closely follow this law.From the law of diffused reflection, it will thus "be seen that a'slight increase in the reflecting co-efflcient makes a -large increasein the light emitted through the window. In my application abovereferred to, the invention is directed broadly to any form of reflectingmedium. I have since found that metallic sodium and potassiumhave very.high reflecting co-efiicients, beingin ;the neighborhood of 99.7. Theirperfect. Substitutingt is value inthe equation for diflused reflection,we get an intensification of approximatelyW at the window, assumingawindow'of 1% area. As explained above, the metallic surface would notfollow exactly the law for difl'used reflection, but would-have a t aluesomewhat less than that obtained by it. As stated above, the bulb couldbe coated with a roughening material or be made with rough and irregularprotuberances so as to more closely follow this law. Since sodium orpotassium oxidize very readily when in the presence of oxygen, it willbe necessary 'to apply the coating with no trace of oxygen. I accomplishthis result as follow. 5:

Referring to Fig. 1, the incandescent bulb 1 which may be glass or metalas in my prior application, is connected to a container 2 by means of atube 3. The container is connected to means for producing a vacuumthrough pipe 4. The vacuum pump or other means is not shown on thedrawing. The container 2 contains the sodium, potassium, or other metal.This container may be a glass tube having restricted ends 3 and 4connected to the bulb and pump respectively. After the incandescentfilament is placed in the lamp, the air is exhausted through the tube 4and the latter sealed. The sodium or other metal in the container 2 isthen heated by any means, a gas jet 5 being shown for the purpose ofillustration. The sodium or other metal is vaporized and passes up intothe lamp bulb Where it is condensed on the interior surface. In order toprevent the metal from condensing on the window 6, heat should beapplied thereto. The window may be heated in any manner but I have showna heating coil 7 closely adjacent there to and connected to a source ofE. M. F. 8. It is also best to send current through the filament 10 inorder to prevent the metal from condensing there. After the metal hascondensed on the interior of the bulb, the glass tube 3 is sealed off inthe usual manner. The bulb is thus provided with a highly reflectingcoating of sodium or other metal with the exclusion of oxygen, and itretains its brilliant surface indefinitely. The lamp, when thus coatedwith sodium or potassium, furnishes a much more concentrated light thanwith all other known reflecting coatings. In order to more efficientlycoat the interior of the bulb, it will be advisable to cool the parts ofthe lamp to which the coat is to be applied. In Fig. 2, I have shownsuch an arrangement. Water or other cooling medium is circulated throughjackets 11, 12, which may be hemispherical. The water jackets are shapedto leave openings for heating coil 7, the connecting plug 13 and thetube 3. With the cooling means shown, the deposit of metal will be moreregular and the window will have a sharper contour. If desired, the lampbulb may be coated while placed in a, draft of cool air to cause thedeposit of metal.

In Fig. 3, I have shown a further method of preventing the metal fromdepositing on a aaeoa the window 6. A disk 14 is. laced in the bulbbefore it is scaled up. T is disk is of the same size as the windowdesired, and is coated on one side with some material such as softvarnish or felt to prevent its scratching the reflecting surface afterthe lamp is complete. Before the sodium or other metal is vaporized,thelamp is turned until the disk 14 slides into the proper position, andthen the air is exhausted and the metal vaporized. The metal willcondense on the interior of the bulb andon the upper surface of the disk14 but it will not condense on the window 6 because it is covered by thedisk. After the coating process is complete, the lamp is turned so thatthe disk 14 slides off the window. In this way the interior of the bulbis coated with sodium or other metal, leaving a sharply defined Windowentirely free from the coating. The reflecting efficiency of the bulb isnot impaired by the disk inasmuch as the upper surface of it is coatedwith reflecting material. handling and in shipping to prevent the diskfrom turning over with the reflecting surface downward. In thisarrangement, current maybe sent through the filaments to prevent themetal from condensing thereon and the bulb may be cooled as in Fig. 2.

In Fig. 4, I have shown a still. further modification. The lamp hereshown is intended for a headlight on automobiles or other carriages. Itconsists of a body portion 15 having a substantially parabolic shape anda transparent portion or window 16. The window 16 may be sealed on tothe body portion 15 in any well known way. The light emitting filamentused in this type of lamp consists of a helix of thin tungsten strip orfoil coiled flatwise with leads 17 and 18 as shown. By using the thinstrip or foil, I am able to concentrate the light source at the focus.The interior of the body portion 15 is to be coated with sodium or othermetal and the window 16 is to be uncoated. As a variation of the methodabove described, I may use mercury, oil or other liquid to prevent themetal from depositing on the window 16. The liquid may be introducedinto the lamp throughtube 19. After the air is exhausted from tube 3,the sodium or other metal in the container 2 is heated and is condensedon the interior of the body portion 15. This body portion may be cooledas previously described. The sodium may be allowed t condense on themercury if such is used, forming an amalgam therewith. After the coatingis applied, the mercury or other liquid is withdrawn through tube 19 andit, as well as tube 3, is sealed. In this way, the sodium is preventedfrom depositing on the window 16. This form of light may be used veryefficiently with dry cells for in- Of course,.care should be used instance. In this modi'fication;- '.,tlie= mercury fact that sodium andpotassiiifni havefveryhigh reflecting co-eflicients, but I :b'elieve Iam the first to disclose the method-described for applying coatings ofsuch; material to the interior of incandescent lamps.

Having described my inventiomf-what I:-

claim is:

1. The process of coating a bulb with a reflecting surface whichconsists in freeing the interior of oxidizing gas, heating a supply ofthe coating material and causing the vapor thereof to condense on theinterior surface of the bulb.

2. The process of coating a bulb-with a reflecting surface whichconsists in freeing the interior of oxidizing gas, heatinga-n externalsupply of the coating material and causing the vapor thereof to condense0n the interior surface of the bulb.

3. The process of coating a bulb with a reflecting surface, whichconsists in freeing the interior of oxidizing gas, leading a supply ofvapor into the interior and causing it to condense on the greater partof the interior surface while preventing it from depositing on theremaining surface.

4. The process of coating a-bulb' with a reflecting surface whichconsists. infreeing the interior of oxidizing gas, heating a portion ofthe bulb, heating a supply of the coating material and causing the vaporthereof to condense on the interior -'surface of said unheated portionof the 5. The process of coating a bulb with a reflecting surface, whichconsists in freeing the interior of oxidizing gas, heating a portion ofthe bulb, cooling the remaining portion and heating a supply of coatingmaterial so that the vapor thereof will condense on the interior surfaceof saidcool of the bulb.

6. The process of making a bulb with reflecting surface whichv consistsin forming the .bulb, roughening the interior surface, freeing theinterior of oxidizing gas, and causing a vapor to condense on theinterior surface. i

7. The process of making an incandescent lamp which consists in formingthe bulb, adding the filament, exhausting, the interior, heating thefilament, and a portion of the bulb andcausing a vapor to condense onthe interior surface of the unheated portion.

8'. The process of making an incandescent lamp which consists in formingthe bulb with" a roughened interior surface, adding the filament,exhausting the interior, heating the filament and a portion of the bulb,and causing a vapor to condense on the in-. terior surface of theunheated portion of the bulb.

9. The process of making an incandescent lamp which consists in formingthe bulb, roughening a portion of the interior surface, adding thefilament exhausting the interior, heating the filament and thenon-roughened portion of the bulb and causing a vapor to condense on thesaid roughened surface.

10. The process of coating a bulb with a reflecting surface whichconsists in freeing the interior-of oxidizing gas, placing a mov ablecover over a portion of the interior surface heatinga supply of thecoating material and causingit to condense on the interior surface ofthe uncovered portion of the bulb. I 1 M In testimonywhereof, I hereuntoaflix my signature in the presence ofwitnesses.

EMERSON L. CLARK.

Witnesses:

IRA J. AnA'Ms, H. G. GROVER.

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